     Sudoku Solution Path   Copyright © Kevin Stone R4C5 can only be <7> R5C4 can only be <6> R5C6 can only be <3> R7C4 can only be <9> R5C1 can only be <9> R6C5 can only be <1> R6C7 can only be <6> R5C5 can only be <8> R6C3 can only be <3> R4C7 can only be <9> R3C4 can only be <5> R4C3 can only be <6> R5C3 can only be <4> R2C2 is the only square in row 2 that can be <5> R1C7 is the only square in row 1 that can be <5> R3C1 is the only square in row 3 that can be <7> R7C8 is the only square in row 7 that can be <7> R9C3 is the only square in row 9 that can be <5> R9C8 is the only square in column 8 that can be <6> Intersection of column 3 with block 1. The value <9> only appears in one or more of squares R1C3, R2C3 and R3C3 of column 3. These squares are the ones that intersect with block 1. Thus, the other (non-intersecting) squares of block 1 cannot contain this value.    R1C2 - removing <9> from <1369> leaving <136>    R3C2 - removing <9> from <139> leaving <13> Intersection of column 8 with block 3. The value <1> only appears in one or more of squares R1C8, R2C8 and R3C8 of column 8. These squares are the ones that intersect with block 3. Thus, the other (non-intersecting) squares of block 3 cannot contain this value.    R1C9 - removing <1> from <1249> leaving <249>    R3C7 - removing <1> from <1238> leaving <238>    R3C9 - removing <1> from <12489> leaving <2489> Squares R2C5 and R2C8 in row 2 and R8C5 and R8C8 in row 8 form a Simple X-Wing pattern on possibility <2>. All other instances of this possibility in columns 5 and 8 can be removed.    R1C5 - removing <2> from <249> leaving <49>    R1C8 - removing <2> from <1239> leaving <139>    R3C8 - removing <2> from <1239> leaving <139>    R9C5 - removing <2> from <234> leaving <34> Squares R9C5 (XY), R9C1 (XZ) and R7C6 (YZ) form an XY-Wing pattern on <2>. All squares that are buddies of both the XZ and YZ squares cannot be <2>.    R7C1 - removing <2> from <236> leaving <36>    R7C3 - removing <2> from <12> leaving <1> R9C1 is the only square in block 7 that can be <2> Squares R1C3<29>, R1C5<49> and R1C9<249> in row 1 form a comprehensive locked triplet. These 3 squares can only contain the 3 possibilities <249>. Since each of the squares must contain one of the possibilities, they can be eliminated from the other squares in the row.    R1C8 - removing <9> from <139> leaving <13> Squares R1C1, R7C1, R1C2 and R7C2 form a Type-4 Unique Rectangle on <36>.    R1C2 - removing <3> from <136> leaving <16>    R7C2 - removing <3> from <346> leaving <46> Squares R1C5 (XY), R3C6 (XZ) and R1C3 (YZ) form an XY-Wing pattern on <2>. All squares that are buddies of both the XZ and YZ squares cannot be <2>.    R3C3 - removing <2> from <29> leaving <9> R1C3 can only be <2> Squares R3C2 and R3C8 in row 3 form a simple locked pair. These 2 squares both contain the 2 possibilities <13>. Since each of the squares must contain one of the possibilities, they can be eliminated from the other squares in the row.    R3C7 - removing <3> from <238> leaving <28> Squares R1C8 and R3C8 in column 8 form a simple locked pair. These 2 squares both contain the 2 possibilities <13>. Since each of the squares must contain one of the possibilities, they can be eliminated from the other squares in the column.    R8C8 - removing <3> from <239> leaving <29> Squares R9C9 (XY), R5C9 (XZ) and R8C8 (YZ) form an XY-Wing pattern on <2>. All squares that are buddies of both the XZ and YZ squares cannot be <2>.    R7C9 - removing <2> from <28> leaving <8> R3C7 is the only square in row 3 that can be <8> Squares R7C6 (XY), R7C7 (XZ) and R9C5 (YZ) form an XY-Wing pattern on <3>. All squares that are buddies of both the XZ and YZ squares cannot be <3>.    R9C7 - removing <3> from <13> leaving <1> R9C9 can only be <9> R5C7 can only be <2> R1C9 can only be <4> R8C8 can only be <2> R1C5 can only be <9> R3C9 can only be <2> R3C6 can only be <4> R5C9 can only be <1> R2C8 can only be <9> R7C7 can only be <3> R7C1 can only be <6> R8C5 can only be <3> R2C5 can only be <2> R7C6 can only be <2> R7C2 can only be <4> R1C1 can only be <3> R9C2 can only be <3> R8C2 can only be <9> R9C5 can only be <4> R3C2 can only be <1> R1C8 can only be <1> R1C2 can only be <6> R3C8 can only be <3> [Puzzle Code = Sudoku-20191206-SuperHard-044209]    